Narrow molecular weight polyester oligomers and method of preparation

ABSTRACT

A polyester composition having an average molecular weight of greater than 450 comprising a most prevalent compound having a main polyester chain containing at least 17 and fewer than 52 carbon atoms and at least 6 and fewer than 18 oxygen atoms, at least 40 weight percent of the molecules of said composition having a molecular weight within 50% of the average molecular weight of the composition. The polyester composition desirably contains at least 1.6 equivalents of unreacted hydroxy groups or at least 1.6 equivalents of unreacted carboxy groups per mole. The composition contains at least four equivalents of ester links in the main chains of the molecules per mole. 
     The composition of the present invention is obtained by the method of the invention wherein alternating series of reactions are each driven essentially to completion where the final molecule of each reaction provides the only available reaction site for the next alternate monomer reaction. The reactions used are the reaction of an anhydride with a hydroxyl to give an ester and a carboxyl group and the reaction of an oxirane group with a carboxyl to give an ester and a hydroxyl group. To start the alternating reaction sequence either a polyol (to react with anhydride) or a polycarboxylic acid (to react with an oxirane) is used.

This is a continuation-in-part of copending patent application Ser. No.854,105 filed Apr. 21, 1986 and issuing as U.S. Pat. No. 4,659,778 onApr. 21, 1987.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to polyester resins used in high solids coatingsand more particularly relates to such a resin having a relatively lowviscosity at high solids concentration. The invention further relates tothe method of manufacturing such a resin.

2. History of the Prior Art

Low molecular weight polyesters have been widely used in high solidscoatings as a binder which will give low volatile organic compounds(VOC) contents when crosslinked with melamine (or urea) formaldehyderesins or isocyanate functional resins. One of the impediments togetting lower volatiles with these polyesters by further reduction inmolecular weight and less solvent (VOC) demand for viscosity reductionis their molecular weight distribution. This problem is discussed inU.S. Pat. No. 4,045,391. As very low molecular weights (500 to 1500 Wn)are approached, the random nature of the polyesterification reactionleaves proportionally larger amounts of the glycols, polyols andpolyacids and their simple esters in the final reaction product. Thesehave sufficient volatility to contribute to the VOCs when tested. Alsothe higher molecular weight portion of the distribution contributes muchmore heavily to the viscosity and resultant solvent demand of thepolyester.

Such polyesters made from oxirane-anhydride single step bulkpolymerizations are known in the prior art. Examples of patentsdescribing such polymerizations are U.S. Pat. Nos. 3,376,272; 3,089,863;2,779,783 and 3,374,208.

Narrowed molecular weight ranges have, however, been difficult to obtaindue to random chain length formation in bulk polymerizations and sincethe temperatures usually associated with esterification reactions causetransesterification and equilibrium reactions.

It has been known that low molecular weight short chain products couldbe obtained by stepwise reaction of oxiranes and anhydrides withrespectively carboxy or hydroxy terminated compounds. Most of suchproducts usually have 20 or fewer combined carbon and oxygen atoms in asingle main chain. Such products which have more than 20 combined carbonand oxygen atoms are still not as good as desired when used asprepolymers due to undesirable properties, e.g. an undesirably highpercentage of volatile components, formation of soft polymers, formationof polymers having a poor combination of hardness and flexibility, or aviscosity lower than desired. In addition, undesirably large amounts ofcrosslinking agents may be required to form a suitable polymer from theprepolymer. Numerous patents describe such low molecular weight, shortchain products, including U.S. Pat. Nos. 3,857,817 and 4,322,508.

U.S. Pat. No. 4,045,391 is directed toward the preparation of lowviscosity polyesters containing fatty acid constituents having anarrowed molecular weight by certain stepwise anhydride-oxiranereactions. The compounds and methods of this patent are not, however,very desirable since the compounds require the presence of ester sidechains which generally reduce weatherability and chemical resistance andincrease color. In addition such side chains are commonly long and causeundesirable resin softness and may reduce reactivity do to hindrance.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the present invention there is provided a polyestercomposition having an average molecular weight of greater than 450 andusually greater than 500 comprising a most prevalent compound having amain polyester chain containing at least 17 and fewer than 52 carbonatoms and at least 6 and fewer than 18 oxygen atoms, at least 40 andusually at least 52 weight percent of the molecules of said compositionhaving a molecular weight within 50 percent of the average molecularweight of the composition, less than 50 and usually less than 40 weightpercent of the molecules of the composition having a molecular weightgreater than 150 percent of the average molecular weight and less than15 and usually less than 8 weight percent of the molecules of thecomposition having a molecular weight less than 50 percent of theaverage molecular weight of the composition. The polyester compositiondesirably contains at least 1.6 equivalents of unreacted hydroxy groupsor at least 1.6 equivalents of unreacted carboxy groups per mole. Thecomposition contains at least four equivalents of ester links in themain chains of the molecules per mole. When the average molecular weightis below 620, the main chains of the molecules usually pass through atleast two equivalents of aromatic groups or branched groups per mole ofcomposition. Each unhalogenated side group of the polyester contains nomore than six carbon atoms and desirably no more than one oxygen atomand each halogenated side group contains no more than nine carbon atoms.The most preferred compositions have side groups of six carbon atoms orless whether or not the side groups are halogenated. At least 80% of themolecules of the polyester composition of the invention contain at leastfour ester groups in the main chain.

The very narrow molecular weight distribution of the composition of thepresent invention is obtained by an alternating series of reactions eachdriven essentially to completion where the final molecule of eachreaction provides the only available reaction site for the nextalternate monomer reaction. These reactions proceed at low temperaturesrelative to esterification to avoid transesterification side reactionswhich would widen the molecular weight distribution. At least twopractical low temperature reaction types are available to give thealternating sequence desired, i.e. the reaction of an anhydride with ahydroxyl to give an ester and a carboxyl group and the reaction of anoxirane group with a carboxyl to give an ester and a hydroxyl group. Tostart the alternating reaction sequence either a polyol (to react withanhydride) or a polycarboxylic acid (to react with an oxirane) can beused.

More specifically, the invention includes a method for manufacturing thecomposition of the invention which method comprises the steps of:

(a) essentially completely reacting a compound A with a compound B;

(b) essentially completely reacting the reaction product of step (a)with a compound C; and

(c) repeating step (b) as often as required to obtain the desired mainchain length, molecular weight and properties, substituting the reactionproduct from the previous step (b) for the reaction product of step (a).

A is a diol or triol of from 2 to 10 carbon atoms or a dicarboxylic ortricarboxylic acid of from 4 to 10 carbon atoms. B is an anhydride of upto 10 carbon atoms or an oxirane of up to 10 carbon atoms, provided thatwhen A is a diol or triol, B is an anhydride and when A is a carboxylicacid, B is an oxirane. C is an anhydride of up to 10 carbon atoms or anoxirane of up to 10 carbon atoms provided that when the reaction productof the previous step is hydroxy terminated, C is an anhydride and whenthe reaction product of the previous step is carboxy terminated, C is anoxirane. "As often as required" in (c) means repeating (b) 0 to 6 timesand stopping when the desired properties are obtained.

DETAILED DESCRIPTION OF THE INVENTION

"Average molecular weight" as used herein means number average molecularweight unless otherwise indicated. Average molecular weight isabbreviated W_(n).

"Equivalents" means equivalent weight.

"Mole" as applied to the compositions of the invention is calculated onthe basis of number average molecular weight or theoretical molecularweight.

"Main chain" means the chain of a molecule which contains the largestnumber of atoms, when the molecule is trifunctionally terminated theatoms in all chains to the terminal functionalities would be considered.

"Aromatic groups" as used in connection with inclusion in a main chainincludes the moieties ##STR1## wherein R is a side group.

"Side group" means a group which may or may not have a terminalfunctional group and does not form part of the main chain, which isconnected to an atom in the main chain. The most common side groups arehydrogen, halogen, lower alkyl and halogenated lower alkyl. Side groupsmay be interconnected to form cyclic structures with atoms of the mainchain, e.g. aromatic groups as previously described.

"Lower alkyl" means alkyl of one to nine carbon atoms.

"Polydispersity" is the weight average molecular weight divided by thenumber average molecular weight. Polydispersity is an indication of thebreadth of molecular weight distribution. Generally, the lower thepolydispersity, the narrower the molecular weight range.

The most prevalent compound in the compositions of the present inventionusually has a molecular weight within 25% of the average molecularweight of the composition and has the structural formula:

    R.sub.3 --R.sub.2 --.sub.n R.sub.1 --R.sub.2 --.sub.n R.sub.3

R₁ is independently at each occurrence, a carbon terminated group towhich may be attached an additional [R₂ ]_(n) R₃ series;

R₂ is independently at each occurrence ##STR2##

R₃ is --H;

R₄ is a hydrogen or a pendant group of up to 6 carbon atoms; providedthat two R₄ groups on adjacent carbon atoms may be combined to form acyclic structure and further provided that R₄ may be up to 9 carbonatoms when R₄ is haloalkyl;

n is independently at each occurrence an integer of 1 to 4. It is to beunderstood that R₂ can be attached to the compound by either end,depending upon the group to which it is attached. The compound containsat least 4 ester links in the main chain.

The compositions of the present invention are particularly suitable ascrosslinking agents, prepolymers and intermediates for reaction withpolyfunctional compounds to form long chain or crosslinked polymericstructures. The carboxy terminated compositions of the present inventioncan, for example, be reacted with oxiranes or polyols to form long chainpolyesters; with phenol formaldehyde, urea formaldehyde or melamineformaldehyde resins to form thermoset plastics; and with epoxies to formcrosslinked expoxy resins. The hydroxy terminated compositions of theinvention can, for example, be reacted with anhydrides or carboxylicacids to form long chain polyesters; with urea formaldehyde and melamineformaldehyde resins; and with polyisocyanates to form polyurethaneresins.

The compositions of the present invention are especially desirablebecause they have a low solvent demand because of their narrow molecularweight range. The compositions are thus excellent for use in curabletype coatings, e.g. polyester based baking enamels. The low solventdemand is desirable for at least two reasons, i.e. it avoids solventwaste and it reduces pollution problems. In addition, the compositionsof the present invention have a low solvent demand while avoiding thepresence of a large percentage of volatile low molecular weightmolecules in the composition.

The compositions of the present invention have an average molecularweight greater than 450, usually greater than 500 and often greater than620. It has been found that compositions having lower molecular weightsare not as suitable for the manufacture of resins. The lower molecularweight compositions usually result in polymers which are not as tough asdesired, i.e. they do not have a good combination of hardness andflexibility. In accordance with the present invention, in order toobtain sufficient toughness, compositions having a molecular weightbetween 450 and 620 desirably contain molecules whose main chains passthrough at least 1.2 and usually two aromatic rings or branch chains.Or, stated otherwise, the composition should contain at least 1.2equivalents of aromatic rings or branches, i.e. tertiary carbon atoms inthe main chains per mole of composition. This goal is usually met byusing phthalic anhydride or trimellitic anhydride as at least one of thereactants in preparing the composition. When branching is used, e.g. bymeans of trimellitic anhydride, at least 5% of the molecules contain atleast one side branch.

The side groups of the composition of the present invention arerestricted to short chain groups, i.e. no more than nine carbon atoms inlength and usually no more than six carbon atoms in length. When sidechains of over six carbon atoms are used, the groups are usuallyhalogenated for improving flame retardance. Long side chains aregenerally undesirable since they do not improve and often decrease thestructural performance of the composition, increase viscosity thusincreasing solvent demand and may hinder reactivity. Side groups may becombined with each other to form cyclic structures in conjunction withatoms in the main chain.

In general, the method of the present invention used to preparecompounds of the present invention comprises the following steps:

(a) essentially completely reacting a compound A with a compound B;

(b) essentially completely reacting the reaction product of step (a)with a compound C; and

(c) repeating step (b) as often as required to obtain the desired mainchain length, molecular weight and properties, substituting the reactionproduct from the previous step (b) for the reaction product of step (a).

A is a diol or triol of from 2 to 10 carbon atoms or a dicarboxylic ortricarboxylic acid of from 4 to 10 carbon atoms. B is an anhydride of upto 10 carbon atoms or an oxirane of up to 10 carbon atoms, provided thatwhen A is a diol or a triol, B is an anhydride and when A is acarboxylic acid, B is an oxirane. C is an anhydride of up to 10 carbonatoms or an oxirane of up to 10 carbon atoms provided that when thereaction product of the previous step is hydroxy terminated, C is ananhydride and when the reaction product of the previous step is carboxyterminated, C is an oxirane.

Examples of suitable di- or trifunctional compounds which may be used ascompound A, i.e. as the initiator, are ethylene glycol, propyleneglycol, 1,4-butanediol; 1,6-hexanediol; 1,8-octanediol; neopentylglycol; 1-3 butanediol; 2,2,4-trimethyl-1,3-pentanediol; water; maleicacid; succinic acid; malonic acid; adipic acid; azelaic acid; sebasicacid; phthalic acid; isophthalic acid; terephthalic acid;hexahydrophthalic acid; tetrahydrophthalic acid; glycerine;trimethylolpropane; trimethylolethane; pentaerythritol; cyclo-hexanedimethanol; ditrimethylol propane; dipropylene glycol; and trimelliticacid. It is to be understood that compound A may itself contain one ormore ester groups and may be prepared by reaction of a polyhydroxy,polycarboxy, polyhydroxy-carboxy containing compound with an oxirane oranhydride to form a polyfunctional hydroxy compound or a polyfunctionalcarboxy compound. Examples of suitable polyhydroxy-carboxy compounds arehydroxy propionic acid, malic acid, citric acid and dimethylol propionicacid.

Examples of suitable difunctional compounds which may be used ascompounds B or C are the anhydrides maleic anhydride; succinicanhydride; phthalic anhydride; tetrahydrophthalic anhydride;hexahydro-phthalic anhydride; butane succinic anhydride; trimelliticanhydride; glutaric anhydride; itaconic anhydride; chlorendic anhydride;methyl hexahydrophthalic anhydride; and methyl tetrahydrophthalicanhydride; and the oxiranes, e.g. ethylene oxide; propylene oxide;butylene oxide; cyclohexene oxide; styrene oxide; butyl glycidyl ether;glycidyl acrylate; glycidyl methacrylate; and glycidyl ether. Phthalicanhydride and propylene oxide are especially suitable for use inaccordance with the present invention.

In carrying out the reaction, between one and two moles of compound Bare reacted with compound A and usually two moles of compound B arereacted with compound A in step (a). Similarly, between one and two andpreferably two moles of compound C are reacted with one mole of thereaction product of step (a) or (b). Preferably the number of moles of Bwhich are reacted per mole of A is the same as the functionality of A.

The reaction in all steps is usually carried out below 200° C.,preferably below 180° C. and most preferably below 150° C. to avoid sidereactions which increases the molecular weight dispersion.

In general, the compositions of the invention are prepared by alternatestepwise additions using 2 to 8 steps and preferably 3 to 7 steps. Thereis usually no cooling between steps. Each step usually requires areaction time of from 1 to 5 hours with anhydride additions commonlytaking from 1 to 2 hours and oxirane additions commonly taking more than4 hours. The toala process time is desirably less than 20 hours.

In the oxirane addition steps, where oxirane is added to thepolycarboxylic acid (2-3 carboxy groups), the oxirane is added inincrements. A catalyst is frequently used in this step to increasereaction speed and reduce reaction temperature. Preferred catalysts aretetramethyl ammonium bromide and triphenyl phosphine. Such catalysts aregenerally added in an amount of from 0.1 to 1 weight percent. Althoughusually not preferred, other catalysts such as dimethylethanolamine maybe used. This step may be carried out at any pressure from atmosphericto greater than 20 Kg/cm².

In the anhydride addition step wherein anhydride is added to a polyol(2-3 hydroxy groups), the anhydride may either be added in increments orall at once. Catalysts are usually not required for the anhydrideaddition step but may optionally be used.

The number of atoms in the carbon oxygen continuous chain between thehydrogens of the terminal functional groups (hydroxyl or carboxyl) arecounted and used to define the polyester chain length. Thus, allanhydride additions to the chain would usually contribute four carbonsand an oxygen since all common cyclic anhydrides have a five-memberedring. An exception is glutaric anhydride with a six-membered ring, butit is rarely used and expensive. All oxirane additions would contributetwo carbons and an oxygen to the continuous chain, since theirthree-membered ring is composed of two carbons and an oxygen. Generally,the energy released by the ring opening is used to drive each additionstep to completion.

All atoms pendant to the continuous chain would not be counted in thechain length. The molecular weight of the polyester molecule would becomposed of the continuous chain and all pendant atoms including theterminal hydrogens of the functional hydroxyls. The molecular weight ofthe oligomer or polyester would vary according to the amount and natureof the pendant groups. An example of a reaction in accordance with thepresent invention, having a cyclic pendant group, is described belowwherein a mole of phthalic anhydride and a mole of propylene oxide areadded to a polyester oligomer chain. ##STR3## Thus, the encircledcontinuous chain in the above addition would include the two carbonylcarbons and the two in-between carbon atoms which are part of thebenzenoid ring as well as the ether oxygen of the anhydride. Alsoincluded would be the two ring carbons of the propylene oxide as well asthe oxirane oxygen. The pendant atoms that would not be included in themain chain would therefore be the remaining carbons of the phthalicanhydride benzoid ring and their attached hydrogens as well as the threehydrogens and methyl group of the propylene oxide. In cases such asthis, where the pendant four remaining carbons from the benzoid ring ofthe phthalic anhydride ring are attached to the continuous chain in twodifferent places, the shortest chain path (2 carbons) shall be thecontinuous main chain of definition. Thus, this scheme can be used todescribe a variety of oxirane and anhydride functional reactants.

A step in the described reactions to prepare the polyester representsthe addition of at least one and preferably two or more moles ofanhydride or, alternatively, at least one and preferably two or moremoles of oxirane to the already-formed polyester oligomer. The moles ofreactant thus added would be two or more, depending correspondingly onwhether the initiating species had a functionality of two or more. Ifsome alternate way was found to incorporate an additional terminatedgroup a carboxyl or hydroxyl to the chain such as through the reactionof trimellitic (anhydride) or glycidol (oxirane), then the reactantmoles of the subsequent step of anhydride or oxirane would becorrespondingly increased. One would thus add a reactive hydroxyl orcarboxyl functional branch to the polyester oligomer. When suchbranching is used to improve the properties of the product, at least 5%and desirably at least 10% of the molecules contain at least one sidechain branch resulting from a trifunctional reactant, e.g. trimelliticanhydride, residue. In such a case with reactive branched oligomers, thelongest continuous chain would define the composition for our purposes.The finished composition would almost always have a functionality of atleast 1.6 and usually at least 1.8.

An initiating species for the subsequent steps in the reaction is areactant having two or more reactive hydroxyl or carboxyl groups capableof reacting with oxiranes or anhydrides. Thus, an initiator with tworeactive groups would give a resultant linear polyester oligomer. Threegroups would lead to an oligomer with one branch and four groups to twobranches, etc. If water were to be used as an initiating species with ananhydride, it would be considered to have a mono-functional hydroxyl.

The polyester oligomers are prepared by addition to an initiatingspecies of a series of alternating oxirane and anhydride (or vice versa)steps reacted essentially to completion, i.e. at least 70% andpreferably at least 90% completely reacted, such that the finalpolyester oligomers would have essentially identical molecular speciesor a molecular weight distribution substantially narrowed. Substantiallynarrowed is in comparison to a polyester oligomer composition derived bythe process wherein, the same reactant amounts are all mixed together atonce and subjected to esterification conditions.

On a linear polyester oligomer the addition of an anhydride and analternate subsequent oxirane step (one mole of each on each side of theinitiating species) would increase the chain length twelve carbons andfour oxygens (6 and 2 on each side).

The minimum chain length shall be defined as containing at leastseventeen carbon atoms and six oxygens between the hydrogens of the tworeactive functionalities (hydroxyl or carboxyl). The actual molecularweight of such an oligomer would range upward from 450 and usually 500depending upon the size of the pendant groups.

The maximum chain length shall be defined as having no more than 52carbon atoms and 18 oxygen atoms (7 or 8 steps) in the continuous chain.The preferred maximum would be 45 carbons and 14 oxygens, representingabout six steps in the reaction.

In general, oligomers below the minimum chain length have too high afunctional content (hydroxyl or carboxyl) and require too muchcrosslinking resin content (hexamethyoxymethylol melamine resin, etc.)to react them completely into the crosslinked polymer network to producethe best film properties. Inferior properties such as brittleness mayalso result from the crosslinked sites being too closely spaced togetherin the network. One may note that the lower limit on chain length andmolecular weight is higher than that which would be calculated forspecific examples in such patents as Henshaw U.S. Pat. No. 3,857,817,e.g., one mole of propylene glycol plus 2 moles of succinic anhydrideplus a subsequent stepwise two moles of propylene oxide or also one moleof azelaic acid plus 2 moles of propylene oxide. It is also higher thanthe examples in Peng U.S. Pat. No. 4,322,508 showing one mole oftrimethylol propane (TMP) plus three moles of phthalic anhydride plusthree moles of propylene oxide added stepwise. While one may increasethe molecular weight and thus lower the functionality of such shortcontinuous chain oligomers with a high proportion of bulky pendantgroups such as greater than six carbon species this produces crosslinkedpolymer networks of recognized inferior properties in thehardness/flexibility balance and durability.

For the upper chain length limit on our claims one encounters adiminishing return with increased length on the lowered viscosity andresultant VOC in coatings of such oligomers made with our disclosures.Also at the upper limit the reactive functionality is lower for thelinear species and the resultant crosslink density of the polymerbecomes lower than desired unless reactive functionality containing sidechains are introduced. Such side chain content tends to increaseviscosity disproportionately, however, with reduced VOC advantages forthe oligomer.

The number of carbon atoms in a chain pendant group shall usually belimited to six whether such pendant group is connected to the continuouschain in only one place (carbon atom) or in more than one place (twodifferent carbon atoms). The pendant groups may originate with eitherthe anhydride or oxirane reactant. Also ester or amide groups and morethan one ether oxygen should not be included in the six carbon or lessradical such that the chemical resistance would be lowered and theresultant increased molecular weight would cause decreased crosslinkdensity such as in the comparison of alkyd resin properties withpolyester resin properties. Thus, butylene oxide, styrene oxide orcyclohexene oxide could be acceptable oxirane reactants whereas C₈₋₁₀olefin oxide or epoxidized fatty acids or branched monocarboxylic acidshaving a carbon number of 10-15 (e.g. Cardura E™) would not.Alternately, in the anhydride source reactants such as phthalicanhydride, hexahydrophthalic anhydride would be acceptable whereasdodecenyl succinic anhydride and maleinized fatty acids would not, andwould contribute to an inferior hardness/flexibility balance.Preferably, the pendant groups should contain four or less carbons butthis may unduly restrict the choice of reactants available to thepractitioner capable of giving traditional thermoset polyester coatingperformance. However, it should be recognized that some pendant groupssuch as the four aromatic carbons from a phthalic anhydride contributebeneficial properties such as hardness and rigidity to the polyesterchain as they are attached in two places. Reactants containing more thansix pendant, e.g. nine, carbons may be introduced if it is the purposeto introduce some special performance feature to the polyester, such asflame retardancy with chlorendic anhydride.

The initiating species can be water, a polyhydroxy functional molecule,a polycarboxylic acid, or a molecule containing more than one of bothcarboxyl or hydroxyl functionality. The limitation on the initiatorwould be that it should not be so high in molecular weight as to undulychange the polyester nature of the oligomer. For example, the use ofdimer acids (C-32) in a short chain oligomer would give it an undulyhigh aliphatic content or a polyethylene glycol initiator would givediminished chemical resistance and increased water sensitivity. Theinitiator should preferably contain no more than 10 carbon atoms in themain chain. Also a polyester as initiator would undesirably increase themolecular weight distribution contrary to the teachings of the presentinvention.

The initiator may also be composed of a mixture of two or moremolecules, particularly if it is derived to modify properties orintroduce branching in the middle of the chain. For example, a mixtureof neopentyl glycol and TMP could be used. However, if the mixture istoo diverse, the molecular weight distribution may be undesirablyincreased.

The method of the present invention has several significant advantages.In particular, the reactions permit the use of lower temperatures whichavoids undesirable esterification and transesterification reactionswhich undesirably increase the molecular weight distribution which inturn would either increase the volatiles or increase the solvent demandof the resulting product. Such side reactions are especially prevalentin the prior art methods employing proton or Lewis acid type catalysts.

In addition, each step can be driven to completion thus obtaining a highconversion rate. The ability to select the number of steps and stepcomponents generally permits selection of the most prevalent compound inthe end product and permits excellent control of molecular weight.Furthermore, hydroxycarboxy functionality of the end product can beprecisely controlled.

A reaction scheme showing five steps in a method in accordance with thepresent invention is as follows: ##STR4##

The following examples serve to illustrate and not limit the presentinvention. Unless otherwise indicated, all parts and percentages are byweight.

A control white thermosetting enamel paint formula was used to testfilms from some of the various oligomers described in the examples. VOCcontributions from the various oligomers were calculated theoreticallybased on determined NVs ASTM D2369 and determined by ASTM method 3690for paint VOCs.

1. TiO₂ --120 grams

2. Oligomer 100%--105 grams

3. Solvent of above--Amount determines VOC

4. Hexamethoxy methylol melamines--45 grams

5. 40% p-toloene sulfonic acid--1.1 grams

6. Reducing Solvent*--As needed to spray 45 sec.--Amount determines VOC

% of product within molecular weight ranges were determined by gelpermeation chromatography. Reactions were conducted in an inertatmosphere of nitrogen to avoid oxidative side reactions.

EXAMPLE A

A terminal hydroxyl functional propylene succinate propylene phthalate,1,6-hexanediol phthalate propylene succinate propylene oligomerabbreviated HO(PO-SA-PO-PA-1,6-HD-PA-SO-SA-PO)OH was prepared in foursteps as follows. The chain length according to definition would be 30carbons and 10 oxygens with a molecular weight of 846.

To a 3-liter flask were added 139 grams (2.2 moles) of 1,6-hexane-dioland 355 grams (2.4 moles) of phthalic anhydride; the diphthalichalf-ester was formed at 285° F. over a 2-hour period to an acid valueof 266 determined in 20% water and 80% dimethylformamide. To this wasadded 4.5 grams of trimethyl ammonium bromide (TMAB) and 154 grams (2.4moles) of propylene oxide over a 4-hour period at 250° F. to an acidvalue of seven. To this was then added 242 grams or 2.4 moles ofsuccinic anhydride over 11/2 hours at 285° F. to form the half-ester. Tothis was then added 4.5 grams of TMAB and 2.4 moles of propylene oxideover a 4-hour period at 250° F. to an acid value of 9. This oligomermixture was then thinned with 105 grams of isobutyl isobutyrate to anoligomer concentration of about 92% and a viscosity of 138 stokes.

In comparison a theoretically-identical oligomer composition wasprepared by conventional esterification with propylene glycolsubstituted on a molar basis for the propylene oxide as below:

Into a five-liter flask was charged 514 grams (4.30 moles) of1,6-hexanediol, 1290 grams of phthalic anhydride (8.72 moles), 662 grams(8.72 moles) of propylene glycol, 872 grams (8.72 moles) of succinicanhydride, and 662 grams (8.72 moles) of additional propylene glycol.Esterification was conducted at 450° F. with a packed column to retainthe propylene glycol over an 8-hour period during which 327 grams (18.2moles) of water were removed to an acid value of 3. To this was added398 grams of EEP solvent (ethoxy n-propionic acid ethyl ester) to anoligomer concentration of 90%. The acid value was 3 and the viscositywas 185 stokes. When cut in isobutyl isobutyrate (IBIB) to the same 90%oligomer concentration, the viscosity is 192 stokes with 89% determinedNV.

The oligomer solution was tested in a control white thermosetting enamelas previously described. The VOC was calculated to be 2.3 pounds/gallon.When baked 20 minutes at 350° F., the 60° gloss was 97 units and a 1.5mil film gave a 4H pencil hardness with 120 in-lbs direct impact.

Properties were determined for the stepwise vs. the unichargepreparations as follows:

    ______________________________________                                        Property        Stepwise   Unicharge                                          ______________________________________                                        Polydispersity  1.26       1.69                                               Preferred W.sub.n Range                                                       +50% 1269 W.sub.n                                                                             26%    above   53.3%  above                                   -50% 423 W.sub.n                                                                              5%     below   7.7%   below                                   Wt % within range                                                                             69%            39.0%                                          ______________________________________                                    

EXAMPLE B

A terminal hydroxy functional propylene phthalate propylene succinatepropylene adipate propylene succinate propylene phthalate propyleneoligomer abbreviated HO(PO-PA-PO-SA-PO-AA-PO-SA-PO-PA-PO)OH was preparedin five steps as follows. The chain length would be 39 carbons and 12oxygens and the molecular weight 990.

In a three-liter flask was charged 219 grams (1.5 moles) of adipic acidand 14.5 grams of tetramethyl ammonium bromide (TMAB) catalyst. To thiswas added 174 grams (3 moles) of propylene oxide at reflux over a periodof three hours at 285° F. to an acid value of 2. To this was added 300grams (3 moles) of succinic anhydride to form the di-half ester at 250°C. for 11/2 hours to an acid value (in 20% H₂ O 80% DMF) of 227. To thiswas then added 174 grams (3 moles) of propylene oxide at reflux at 250°F. over 21/2 hours to an acid value of 7. To this was then added 444grams (3 moles) of phthalic anhydride at 260° F. for four hours to anacid value of 137 N,N-dimethyl formamide (DMF). To this was then added174 grams (3 moles) of propylene oxide at 270° F. and the mixture wasrefluxed over a 21/2 hour period until an acid value of 4 was reached.1225 grams of this oligomer was then reduced with 136 grams of EEP to anoligomer content of 90% and a viscosity of 79 stokes.

For comparison, a theoretically compositionally identical oligomer wasprepared by conventional esterification procedures with propylene glycolsubstituted for propylene oxide on a molar basis as below:

Into a five-liter flask was charged all together 2.43 times each of thefollowing ingredients: 219 grams (1.5 moles) of adipic acid; 228 grams(3 moles) of propylene glycol; 300 grams (3 moles) of succinicanhydride; 228 grams (3 moles) of propylene glycol; 444 grams (3 moles)of phthalic anhydride; and 228 grams (3 moles) of propylene glycol. Thiswas esterified at 460° F. for 9 hours under a packed column until anacid value of 5. This was then reduced to 90% oligomer content with EEPwith a viscosity of 300 stokes. It can be noted that this viscosity isalmost three and a half times that of the oligomer prepared by theprocess of the invention in the same solvent at the same oligomercontent.

The stepwise oligomer was tested in the control paint formula and gave acalculated VOC of 2.3 lbs/gal. and a determined ASTM 3960 VOC of 2.66.When baked at 350° F. for 20 minutes, 1.5 mil films gave a 60° gloss of96% and 2H pencil hardness with 80 in-lbs direct impact resistance.

    ______________________________________                                        Property       Stepwise    Unicharge                                          ______________________________________                                        Polydispersity 1.55        1.81                                               Preferred W.sub.n Range                                                       +50% 1483 W.sub.n                                                                            16.9%   above   50.0%  above                                   -50% 495 W.sub.n                                                                             6.2%    below   9.5%   below                                   Wt % within range                                                                            76.9%           41.5%                                          ______________________________________                                    

EXAMPLE C

A terminal dihydroxy functional propylene mixed succinate phthalate1,6-hexane mixed succinate phthalate propylene polyester oligomerabbreviated HO(PO.SA/PA.1,6-HD.SA/PA.PO)OH was prepared in five steps asfollows. The chain length of the theoretical oligomer would be 18carbons and 6 oxygens and the molecular weight would be 520.

To a five-liter flask was charged 708 grams of 1,6-hexanediol (6 moles),1598 grams (10.8 moles) of phthalic anhydride and 120 grams (1.2 moles)of succinic anhydride. This was held at a temperature of 270° F. forabout two hours to an acid value of 264 in DMF. To this was then added15.6 grams of triphenyl phosphine catalyst and 697 grams (12 moles) ofpropylene oxide under reflux over a period of five hours to an acidvalue of 13. An additional 12 grams of propylene oxide was added toreplace losses from the condensor at 270° F. for an hour to furtherreduce the acid value to nine. To 2903 grams of this was added 153 gramsof EEP solvent to a 95% oligomer concentration with a viscosity of 121stokes and a hydroxyl value of 189 and a determined non-volatile of93.4%.

As a comparison, a theoretically-identical oligomer composition (exceptfor molecular weight distribution) was prepared by conventionalpolyesterification techniques. Propylene glycol is substituted on amolar basis for the propylene oxide.

The following ingredients were all charged together to a five-literflask with a packed column: 974 grams (8.25 moles) of 1,6 hexanediol,2200 grams (14.9 moles) of phthalic anhydride, and 1255 grams (16.5moles)S of propylene glycol. These were esterified under reflux at 420°F. for eleven hours to an acid value of six, evolving 300 grams (16.5moles). Ninety-five grams of this oligomer was reduced with 5 grams ofEEP solvent to an oligomer content of 95%, a viscosity of 190 stokes, adetermined NV of 89.6%, and a hydroxyl value of about 198. When comparedto the above oligomer of our disclosed procedures, the lower determinedNV (89.6 versus 93.4%) indicates considerably more lower molecularweight species and the higher viscosity D(190 stokes versus 121 stokes)considerably more higher molecular weight species for theconventionally-prepared polyester and thus a narrower molecular weightdistribution with the disclosed procedures.

When the stepwise oligomer was tested in the control paint, a calculatedVOC of 2.1 lb/gal was obtained and a determined (ASTM 3960) VOC of 2.3was obtained. When baked 20 minutes at 350° F. 1.5 mil paint films had a60° gloss of 79 and a 2H pencil hardness with a 40 in-lbs direct impactresult.

    ______________________________________                                        Property       Stepwise     Unicharge                                         ______________________________________                                        Polydispersity 1.17         1.45                                              Preferred W.sub.n Range                                                       +50% 780 W.sub.n                                                                             16.7%   above    54.4% above                                   -50% 260 W.sub.n                                                                             3.0%    below    4.3%  below                                   Wt % within desired range                                                                    70.3%            43.3%                                         ______________________________________                                    

EXAMPLE D

A terminal hydroxy-functional propylene mixed succinate phthalatepropylene, mixed succinate phthalate, dipropylene glycol, mixedsuccinate phthalate, propylene mixed succinate phthalate, propylenepolyester oligomer abbreviated

    HO(PO.SA/PA.PO.SA/PA.DPG.SA/PA.PO.SA/PA.PO)OH

was prepared in four steps as follows. The oligomer chain length wouldbe 28 carbons and 8 oxygens and the theoretical molecular weight 862.

To a three-liter flask was charged 268 grams (2 moles) of dipropyleneglycol, 200 grams (2 moles) of succinic anhydride and 296 grams (2moles) of phthalic anhydride. This was reacted at 260° F. for 21/2 hoursto an acid value of 293 (in DMF). To this was added seventeen grams oftrimethyl ammonium bromide catalyst and 232 grams (4 moles) of propyleneoxide under reflux over a period of six hours at about 250° F. to anacid value of six. To this was then added 200 grams (2 moles) ofsuccinic anhydride and 296 grams (2 moles) of phthalic anhydride andthis was reacted at 285° F. to an acid value of 153 (in H₂ O.DMF) over aperiod of three hours. To this was added 232 grams (4 moles) ofpropylene oxide under reflux at about 250° F. over a period of fivehours to an acid value of five.

Nine hundred grams of this oligomer was then reduced with a hundredgrams of EEP solvent to a viscosity of 138, hydroxyl value of 105 and adetermined VOC of 89%.

As a comparison, a theoretically identical oligomer composition (exceptfor molecular weight distribution) was prepared by conventionalpolyesterification techniques. Propylene glycol was substituted on amolar basis for the propylene oxide. To a five-liter flask with a packedcolumn the following were charged all together: 536 grams (4 moles) ofdipropylene glycol; 800 grams (8 moles) of succinic acid; 1184 grams (8moles) of phthalic anhydride; and 1216 grams (16 moles) of propyleneglycol. This was reacted under reflux at 450° F. for seven hoursevolving 270 grams of water to an acid value of 6. To 900 grams of thisoligomer 100 grams of EEP solvent was added for a viscosity of 262stokes and a hydroxyl value of 103. It may be noted that the viscosityis twice that of the oligomer prepared by the methods of the presentinvention.

The stepwise oligomer, when tested in the control paint, gave adetermined (ASTM 3960) VOC of 2.35 lb/gal. When baked at 350° F. for 20minutes, the 60° gloss was 97% for 1.5 mil films with 3H pencil hardnessand 60 inch/lbs direct impact resistance. In contrast, the unichargeoligomer gave a 2.72 lb/gal determined VOC (ASTM 3960) with essentiallythe same film qualities.

Molecular weight distribution properties are as follows:

    ______________________________________                                        Property       Stepwise    Unicharge                                          ______________________________________                                        Polydispersity 1.28        1.64                                               Preferred W.sub.n Range                                                       +50% 1293 W.sub.n                                                                            22.1%   above   44.5%  above                                   -50% 431 W.sub.n                                                                             7.5%    below   9.0%   below                                   Wt % within range                                                                            70.4%           46.5%                                          ______________________________________                                    

EXAMPLE E

A terminal hydroxy functional propylene mixed phthalate succinate,dipropylene glycol, mixed phthalate succinate, propylene polyesteroligomer, abbreviated:

    HO(PO.PA/SA.DPG.PA/SA.PO)OH

was prepared in two steps as follows. The chain length of the oligomersis 16 carbons and seven oxygens and the theoretical molecular weightwould be 498.

To a three-liter flask was charged 469 grams (3.5 moles) of dipropyleneglycol, 350 grams (3.5 moles) of succinic anhydride and 518 grams (3.5moles) of phthalic anhydride and reacted at 280° F. for 11/2 hours to anacid value of 309 in DMF. To this was added 17 grams of trimethylammonium bromide catalyst and 407 grams of propylene oxide under refluxat 260° F. for 8 hours to an acid value of seven. To 940 grams of theresultant oligomer was added 50 grams of IBIB solvent for a viscosity of51 stokes and a determined NV of 92%.

For comparison a theoretically identical oligomer composition (exceptfor molecular weight distribution) was prepared by conventionalpolyesterification techniques. Propylene glycol was substituted on amolar basis for the propylene oxide. To a three-liter flask equippedwith a packed column condenser was charged 402 grams (3 moles) ofdipropylene glycol; 300 grams (3 moles) of succinic anhydride; 444 grams(3 moles) of phthalic anhydride; and 456 grams (6 moles) of propyleneglycol. This was reacted at reflux at 450° F. for five hours to an acidvalue of six evolving 103 grams of water. To 94 grams of oligomer wasadded six grams of IBIB solvent for a viscosity of 43 stokes and adetermined NV of 87%. While the viscosity is not higher than theoligomer of the process of our disclosure, probably due to the largeamount of low molecular weight fractions, the lower determined NV (87%versus 92%) indicates the large amounts of these low molecular weightfractions which are detrimental to determined VOCs on the resultantpaints.

When tested in the control paint, the stepwise oligomer gave acalculated VOC of 2.0 lbs/gal whereas the unicharge oligomer gave acalculated VOC of 2.4 lbs/gal.

    ______________________________________                                        Property       Stepwise     Unicharge                                         ______________________________________                                        Polydispersity 1.20         1.51                                              Preferred W.sub.n Range                                                       +50% 747 W.sub.n                                                                             23.8%   above    48.7% above                                   -50% 249 W.sub.n                                                                             3.0%    below    4.5%  below                                   Wt % within desired range                                                                    73.2%            46.7%                                         ______________________________________                                    

EXAMPLE F

A hydroxyl-terminated propylene mixed succinate phthalate propyleneadipate propylene mixed phthalate succinate propylene polyesteroligomer, abbreviated HO(PO.PA/SA.PO.AA.PO.PA/SA.PO)OH, was prepared asfollows. The chain length would be 22 carbons and 8 oxygens and thetheoretical molecular weight would be 664.

To a five-liter flaks with reflux condenser was charged 879 grams (6.02moles) of adipic acid, 698 grams (12.04 moles) (with 10% excess to allowfor losses through condenser) of propylene oxide and 20 grams oftriphenyl phosphine catalyst. This was reacted (with a gradual additionof the propylene oxide) at reflux and 270° F. for a period of 3 hours toan acid value of one and the excess propylene oxide sparged off withinert gas. To this was then added 1604 grams (10.84 moles) of phthalicanhydride and 120 grams (1.20 moles) of succinic anhydride which wasreacted at 270° F. for 11/2 hours to an acid value 158 (in DMF). Thisproduct was in turn reacted with 698 grams (12 moles) of propylene oxideunder reflux for three hours to an acid value of 7 and a hydroxyl valueof 155. Nine hundred and 50 grams of the resulting oligomer was reducedwith 50 grams of EEP solvent to a viscosity of 213 stokes.

For a comparison, a theoretically identical composition polyesteroligomer was prepared using conventional unicharge esterificationprocedures. Propylene glycol replaced the propylene oxide on a molarbasis.

To a five-liter flask with packed column condenser was charged alltogether 879 grams (6.02 moles) of adipic acid, 1830 grams (24 moles) ofpropylene glycol, 1604 grams of phthalic anhydride (10.8 moles) and 120grams of succinic anhydride (1.2 moles). These were reacted at 450° F.under reflux for 7 hours to an acid value of 10 and a hydroxyl value of150. When 950 grams of this oligomer was reduced with 50 grams of EEPsolvent, the viscosity was 404 stokes about twice that of the oligomerprepared with our disclosures.

As a further example the final propylene oxide reaction step of thestepwise oligomer above was modified with ethylene oxide replacing thepropylene oxide on a molar basis. The chain length of this oligomer isthe same as that of the stepwise propylene oxide oligomer but themolecular weight is reduced to 636. The ethylene oxide was introducedgradually under a pressure of 50 psi, at 250° F. until an acid value of1.4. was obtained.

When 950 grams of this oligomer was reduced with 50 grams of EEPsolvent, the viscosity was 129 stokes.

A control paint was prepared from the stepwise propylene oxide oligomeraccording to the procedures described above and a calculated VOC of 2.1lbs/gal and a determined VOC of 2.3 lbs/gal was obtained. A 60° gloss of90% with an H pencil hardness and 160 inch-lbs of impact resistance from1.5 mil films baked at 15 minutes at 300° F.

When the unicharge oligomer was prepared in the same paint, a calculatedVOC of 2.3 lbs/gal and a determined VOC (ASTM 3960) of 2.7 lbs/gal wasobtained.

    ______________________________________                                        Property       Stepwise    Unicharge                                          ______________________________________                                        Polydispersity 1.25        1.55                                               Preferred W.sub.n Range                                                       +50% 1008 W.sub.n                                                                            18.2%   above   46.5%  above                                   -50% 332 W.sub.n                                                                             7.5%    below   10.2%  below                                   Wt % within range                                                                            74.3%           43.3%                                          ______________________________________                                    

EXAMPLE G

The following theoretical linear polyester oligomer was prepared ineight steps according to our disclosed procedure as below:

A terminal hydroxy-functional propylene, succinate, propylene,succinate, propylene, pthalate, propylene, succinate, 1,6-hexanediol,succinate, propylene, phthalate, propylene, succinate, propylene,succinate, propylene polyester oligomer, abbreviated:

    HO(PO.SA.PO.SA.PO.PA.PO.SA.1,6-HD.SA.PO.PA.PO.SA.PO.SA.PO)OH

was prepared in eight steps as follows. The chain length is 44 carbonsand 16 oxygens and the theoretical molecular weight if 1478.

To a five-liter flask were charged 558 grams (4.73 moles) of1,6-hexanediol and 946 grams (9.46 moles) of succinic anhydride. Thiswas reacted to the di-half ester at 250° F. to an acid value of 356 (inDMF). To this was added 20 grams of triphenyl phosphine, 548 grams (9.46moles) of propylene oxide at reflux at 270° F. over two hours to an acidvalue of six. To this was added 1400 grams (9.46 moles) of phthalicanhydride and reacted at 275° F. for two hours to 173 acid value (DMF)to form the di-half ester. To this in turn was added 548 grams (9.46moles) of propylene oxide to an acid value of 4 under reflux at 265° F.over a four-hour period. At this stage, 2000 grams of oligomer (2.36moles) were transferred to another five-liter flask and the reactioncontinued by the addition of 473 grams (4.73 moles) of succinicanhydride, which was reacted to the di-half ester at 280° F. in 11/2hours to 103 acid value in DMF. To this was added 7.5 grams of triphenylphosphine and 274 grams (4.73 moles) of propylene oxide under reflux at270° F. over a 3-hour period to an acid value of seven. To this was inturn charged 473 grams (4.73 moles) of succinic anhydride and thedi-half ester formed at 280° F. to an acid value of 76 (in DMF). To thiswas added 274 grams (4.73 moles) of propylene oxide over a four-hourperiod at reflux at 265° F. to an acid value of one. Nine hundred gramsof the resultant oligomer was reduced with 100 grams of EEP solvent to231 stokes viscosity with a determined NV of 89.5%.

For comparison, a theoretically identical oligomer composition (exceptfor the molecular weight distribution) was prepared by conventionalpolyesterification techniques. Propylene glycol was substituted on amolar basis for the propylene oxide. To a five-liter flask with a packedcolumn was charged all together 305 grams (2.58 moles) of1.6-hexanediol; 1553 grams (15.53 moles) of succinic anhydride; 1574grams (20.71 moles) of propylene glycol; and 767 grams (5.18 moles) ofphthalic anhydride. This was reacted at 440° F. under reflux for 12hours to an acid value of 2 evolving 363 grams of water. To 900 grams ofthis oligomer were added 100 grams of EEP solvent to 90% oligomerconcentration and a viscosity of 586 with a determined NV of 89.4%. Itcan be noted that this viscosity is approximately twice that of theoligomer prepared with the disclosure of the invention.

When tested in the control paint, the stepwise oligomer had a calculatedVOC of 2.5 lbs/gal in contrast to a calculated VOC of 2.8 for theunicharge oligomer. The pencil hardness and flexibility of these filmswere approximately equal (H and 160 in/lbs impact).

    ______________________________________                                        Property           Stepwise                                                   ______________________________________                                        Polydispersity     1.64                                                       Preferred W.sub.n Range                                                       +50% 2214 W.sub.n  42.1%      above                                           -50% 738 W.sub.n   9.8%       below                                           Wt % within desired range                                                                        48.1%                                                      ______________________________________                                    

EXAMPLE H

A terminal hydroxy functional propylene, phthalate, propylene,phthalate, propylene, succinate, 1,6-hexandiol, propylene, succinate,propylene, phthalate, propylene, phthalate, propylene polyesteroligomer, abbreviated

    HO(PO.PA.PO.PA.PO.SA.1,6-HD.SA.PO.PA.PO.PA.PO)OH,

was prepared in six steps as follows. The chain length is 32 carbons and12 oxygens and the molecular weight is 1258.

To a five-liter flask was added 2000 grams (2.37 moles) of the oligomerformed in the first four steps of Example G. The reaction is continuedwith 700 grams of phthalic anhydride reacted to the di-half ester at290° F. for an hour and a half to an acid value of 103 (in pyridine). Tothis was added 274 grams of propylene oxide under reflux over a periodof 31/2 hours to an acid value of 6 and a hydroxyl value of 83. When 850grams of this oligomer are reduced with 150 grams of EEP solvent to an85% oligomer concentration the viscosity is 149 with a determined NV of89.5%

For a comparison a theoretically identical oligomer composition (exceptfor molecular weight distribution) was prepared by conventionalpolyesterification techniques. Propylene glycol was substituted on amolar basis for the propylene oxide. To a five-liter flask with a packedcolumn condenser was added all together 346 grams (2.93 moles) of 1-6hexanediol; 586 grams (5.86 moles) of succinic anhydride; 1336 grams(17.57 moles) of propylene glycol; and 1743 grams (11.71 moles) ofphthalic anhydride. This, with 27 grams of propylene glycol to replacelosses, was esterified under reflux at 450° F. for 12 hours at an acidvalue of 4 and a hydroxyl value of 70. When 850 grams of this oligomerwere reduced with 150 grams of EEP solvent to 85% oligomer content, aviscosity of 366 stokes with an 84.5% determined NV resulted. This ismore than the viscosity of the oligomer obtained by the procedures ofthese disclosures.

A second conventionally prepared polyester was prepared as describedabove except that the total amount of propylene glycol was increased by137 grams (1.82 moles). The final acid value was 3 and the viscosity was140 stokes when reduced to 85% oligomer content with EEP as above. Thepolydispersity was 1.81. This conventional polyester showed a shift inthe GPC molecular weight distribution downward such that it had adecrease in the amount above the theoretical W_(n) +50% of 46.9% to 26%and an increase in the amount below the theoretical W_(n) -50% of 16.7%to 30%. This shows that compositional changes will not improve theconventionally prepared polyester to that of our disclosure. If themolecular weight is lowered, more volatiles will occur than in a productprepared in accordance with the invention. If the molecular weight israised, the viscosity and more long chain material will occur than in aproduct prepared in accordance with the invention.

    ______________________________________                                                                         Propylene                                                                     Glycol Excess                                Property  Stepwise   Unicharge   Unicharge                                    ______________________________________                                        Polydispersity                                                                          1.19       1.87        1.81                                         Preferred W.sub.n                                                             Range                                                                         +50% 1887 W.sub.n                                                                       24%    above   46.9% above 26%   above                              -50% 629 W.sub.n                                                                        5%     below   16.7% below 30%   below                              Wt % within                                                                             71%            34.4%       44%                                      range                                                                         ______________________________________                                    

EXAMPLE I

In this example, an oligomer is prepared by the method described inExample 2 of U.S. Pat. No. 4,045,391.

To a three-liter flask, 111.4 grams (0.94 mole) of 1,6-hexanediol and279.2 grams (1.89 moles) of phthalic anhydride were charged and reactedat 300° F. for two hours to an acid value of 276 in DMF. To this wasthen added 462 grams (1.89 moles) of C₁₃ carboxylic acid glycidal ester(Cardura E®, Shell) and reacted at 300° F. for three hours to an acidvalue of 9.5. To this in turn was added 279 grams of phthalic anhydridewhich was reacted at 300° F. for 11/2 hours to an acid value of 64(DMF). To this was added 468 grams of ethylene glycol (large excess) andthe acid value reduced to 10 over a six-hour period at 380° F. Theexcess ethylene glycol was distilled off under vacuum at 375° F. forfour hours.

Ninety grams of this oligomer was reduced with 10 grams of butyl acetateto a viscosity of 29 stokes, a determined NV of 87% and a hydroxyl valueof 150. As the theoretical hydroxyl value is 78, one would conclude thatthe distillation of the ethylene glycol is an inefficient method ofpreparing the desired product subject to possible transesterificationcomplications.

EXAMPLE J

In this example, an oligomer is prepared by the method disclosed inExample 5 of U.S. Pat. No. 4,045,391 except that ethylene oxide isreplaced on a molar basis by propylene oxide for convenience inpreparation.

For a three-liter flask equipped with condenser was charged 127 grams(0.87 mole) of adipic acid and 427 grams (1.74 moles) of C₁₃ carboxylicacid glycidal ester (Cardura E®). This was reacted at 310° F. for fourhours to an acid value of 14. To this was added 258 grams (1.74 moles)of phthalic anhydride and the mixture reacted at 300±F. for two hours toan acid value of 125 (in DMF). To this in turn was added 427 grams (1.74moles) of Cardura E® and the mixture reacted at 310° F. to an acid valueof 13 over 21/2 hours. To this in turn was charged 258 grams of phthalicanhydride (1.74 moles) and this was reacted to 94 acid value (DMF) over2 hours. To this in turn was added 101 grams (1.74 moles) of propyleneoxide at 300° F. under reflux over a five-hour period to a 32 acid valueand a 57 hydroxyl value. Ninety grams of this was reduced with 10 gramsof isobutyl isobutyrate solvent to a viscosity of 143 and determined NVof 87%.

The oligomer solution was evaluated in the control white paint. Acalculated VOC of 2.5 lbs/gal and a determined VOC of 2.8 lbs/gal wereobtained. When films were cured with a high bake of 20 minutes at 350°F., only an F pencil hardness was obtained and the coating failed 10in-lbs reverse impact, indicating a film of low strength.

EXAMPLE K

A trifunctional hydroxy-terminal oligomer was prepared which illustratesa technique for introducting branching into the oligomer. The molecularweight and chain length can be increased by additional anhydride andoxirane steps as described herein.

A tripropylene mixed phthalate succinate trimethylol propane oligomerabbreviated ##STR5## was prepared as follows. The largest chain lengthwould be 15 carbons and 6 oxygens and the theoretical molecular weightwould be 707.

The oligomer was prepared by charging 268 grams (2 moles) of TMP, 7grams of triphenyl phosphine catalyst, and 592 grams (4 moles) ofsuccinic anhydride to a flask with condenser and reacting at 280° F.over a 11/2 hour period to an acid value of 304 (DMF). To this was thenadded 349 grams (6 moles) of propylene oxide under reflux at 275° F.over a period of five hours to an acid value of 9. When 85 grams of thisoligomer were reduced with 15 grams of EEP solvent, the viscosity was237 stokes.

As a comparison, a polyester was prepared by conventionalpolyesterification techniques in the following manner. To a flaskequipped with packed column reflux condenser was added all together 268grams (2 moles) of TMP; 592 grams (4 moles) of phthalic anhydride; 200grams (2 moles) of succinic anhydride; and 456 grams (6 moles) ofpropylene glycol. This was reacted at reflux at 450° F. for 6 hours toan acid value of 8 and a hydroxyl value of 222. When 85 grams of thisoligomer were reduced with 15 grams of EEP, a viscosity of 400 stokeswere obtained.

EXAMPLE L

A terminal dihydroxy functional propylene phthalate 1-6 hexane phthalatepropylene polyester oligomer abbreviated as HO(PO.PA-1,6.HD.PA-PO)OH,was prepared in two steps as follows. The chain length is 18 carbons andsix oxygens and the theoretical molecular weight would be 530.

To a five-liter flask with condenser was charged 890 grams (7.54 moles)of 1,6 hexanediol and 2234 grams (15.09 moles) of phthalic anhydride.This was reacted at 285° F. (approx.) for a period of forty minutes toan acid value of 288 in DMF. To this was added 24 grams of triphenylphosphite at 275° F. and then 876 grams (15.1 moles) of propylene oxideunder reflux over a period of five hours to an acid value of 4.3 and ahydroxyl value of 203. Ninety-five grams of this polyester was reducedwith 5 grams of EEP solvent to give a viscosity of 98 and a determinedNV of 92.2. The polydispersity is determined to be 1.12.

In order to compare a chemically theoretically identical oligomer(except for molecular weight distribution) by conventionalpolyesterification reaction, the following ingredients were all chargedtogether in a five-liter flask equipped with a packed column condenser.Propylene glycol replaces propylene oxide on a molar basis. Thisincluded 890 grams of 1,6 hexanediol (7.54 moles), 2234 grams (15.1moles) of phthalic anhydride, and 1148 grams (15.1 moles) of propyleneglycol which was heated to 425° F. and refluxed while removing water ofreaction over a 71/2 hour period to an acid value of 5.1 and a hydroxylvalue of 206. Ninety-five grams of this polyester were then reduced withfive grams of EEP solvent to a viscosity of 334 and a determined NV of89.5%. The polydispersity was reported as 1.48.

The molecular weight distribution properties are as follows:

    ______________________________________                                        Property        Stepwise    Unicharge                                         ______________________________________                                        Polydispersity  1.12        1.48                                              Preferred W.sub.n Range                                                       +50% 795 W.sub.n                                                                              15.2%   above   56%   above                                   -50% 265 W.sub.n                                                                              1.7%    below   4%    below                                   Wt % within range                                                                             83.1%           40%                                           ______________________________________                                    

EXAMPLE M

A terminal dihydroxy functional propylene, phthalic, propylene adipate,propylene, phthalate, propylene, polyester oligomer, abbreviatedHO(PO.PA.PO.AdA.PO.PA.PO)OH, was prepared in three steps as follows. Thechain length of the theoretical oligomer is 22 carbons and 8 oxygens andthe theoretical molecular weight is 672.

To a three-liter flask with reflux condenser was charged 292 grams (2.0moles) of adipic acid and 5.3 grams of TMAB catalyst. To this was added232 grams of propylene oxide over a period of 18 hours at 225° F. to anacid value of 3. To this was added 592 grams (4.0 moles) of phthalicanhydride over a period of an hour at 275° F. to an acid value of 205(DMF). To this was added 232 grams (4.0 moles) of propylene oxide over aperiod of 3 hours at 250° F. under reflux to an acid value of 7 and ahydroxyl value of 148. Ninety grams of this polyester were reduced withisobutylisobutyrate solvent (IBIB) to an 88.1 determined NV and aviscosity of 75 stokes. The polydispersity was reported as 1.27.

As a comparison, a chemically equivalent theoretically identicaloligomer composition (except for Mwt distribution) was prepared byconventional polyesterification technique with propylene glycolreplacing propylene oxide on a molar basis.

To a five-liter flask equipped with a packed column condenser wascharged all together 585 grams (4.0 moles) of adipic acid, 1216 grams(8.0 moles) of propylene glycol, and 1184 grams (8.0 moles) of phthalicanhydride. This was then heated to 460° F. for 6 hours under reflux toan acid value of nine, removing 132 grams of water. When reduced (95grams) with five grams of IBIB, the viscosity was 554 stokes and adetermined NV of 92.3%. The polydispersity was reported as 1.56.

The molecular weight distribution properties are as follows:

    ______________________________________                                        Property        Stepwise    Unicharge                                         ______________________________________                                        Polydispersity  1.27        1.56                                              Preferred W.sub.n Range                                                       +50% 1008 W.sub.n                                                                             23.7%   above   49%   above                                   -50% 336 W.sub.n                                                                              7.0%    below   9%    below                                   Wt % within range                                                                             69.3%           42%                                           ______________________________________                                    

EXAMPLE N

A terminal dihydroxy functional ethylene mixed succinate phthalatepropylene adipate propylene mixed succinate phthalate ethylene polyesteroligomer abbreviated

    HO(EtO.SA/PA.PO.AdA.PO.SA/PA.EtO)OH,

was prepared in three steps as follows. The chain length of thetheoretical oligomer would be 22 carbons and 8 oxygens, and themolecular weight would be 634.

To a five-liter flask equipped with a reflux condenser was added 879grams of adipic acid and 20 grams of triphenyl phosphine catalyst andheated to 280° F. To this was added 698 grams (12 moles) of propyleneoxide over a 6-hour period at 260° F. to an acid value of one. To thiswas then added 1604 grams (10.8 moles) of phthalic anhydride and 120grams of succinic anhydride and reacted at 280° F. for two hours to anacid value of 196. To this was added 528 grams (12 moles) of ethyleneoxide under 50 psi pressure at 250° F. for 3 hours to an acid value of1.3 and a hydroxyl value of 167. When 85 parts of this was reduced withfive parts of EEP, a viscosity of 129 stokes at a predetermined NV of94.0 was obtained. The polydispersity was reported at 1.24.

As a comparison, a theoretically and chemically identical polyesteroligomer (except for molecular weight distribution) was prepared byconventional polyesterification techniques. Ethylene glycol was used toreplace the ethylene oxide and propylene glycol to replace the propyleneoxide.

The following materials were all charged together to a five-liter flaskequipped with a packed column reflux condenser. This included: 692 grams(4.74 moles) of adipic acid; 720 grams (9.48 moles) of propylene glycol;1262 grams (8.53 moles) of phthalic anhydride; 95 grams (0.95 mole) ofsuccinic anhydride; and 588 grams of ethylene glycol. This was thenheated to 495° F. over a 7-hour period under reflux to a 6.7 acid valueand a 167 hydroxyl value. When 95 parts of this was reduced with fiveparts of EEP, the viscosity was 214 stokes at a determined NV of 93.0%.The polydispersity was reported as 1.56.

The molecular weight distribution properties are as follows:

    ______________________________________                                        Property       Stepwise    Unicharge                                          ______________________________________                                        Polydispersity 1.24        1.56                                               Preferred W.sub.n Range                                                       +50% 951 W.sub.n                                                                             23.0%   above   47.7%  above                                   -50% 317 W.sub.n                                                                             5.8%    below   10.6%  below                                   Wt % within range                                                                            71.1%           41.7%                                          ______________________________________                                    

A control white thermosetting enamel was prepared for both of the aboveoligomers. The paint based on the above polyester of our disclosure hada measured VOC of 2.50 lbs/gal as compared to a measured VOC of 2.89lbs/gal for the paint based on the above conventionally preparedpolyester control. The film properties when cured as per Example A wereessentially equivalent except for an improved flexibility (100%) for thepolyester of our disclosure.

What is claimed is:
 1. A polyester composition having an averagemolecular weight of greater than 450 comprising a most prevalentcompound having a main polyester chain containing at least 17 and fewerthan 52 carbon atoms and at least 6 and fewer than 18 oxygen atoms, atleast 40 weight percent of the molecules of said composition having amolecular weight within 50% of the average molecular weight of thecomposition; less than 50 weight percent of the molecules of thecomposition having a molcular weight greater than 150% of the averagemolecular weight of the composition and less than 15 weight percent ofthe molecules of the composition having a molecular weight less than 50%of the average molecular weight of the composition, said polyestercomposition containing at least 1.6 equivalents of unreacted hydroxygroups or at least 1.6 equivalents of unreacted carboxy groups per mole;at least 5% of the molecules containing at least one side chain branchresulting from a trimellitic anhydride residue, and said compositioncontaining at least four equivalents of ester links in the main chainsof the molecules per mole of composition, said composition containingside groups selected from hydrogen and halogenated and unhalogenatedgroups attached to the main chain through a carbon atom, each of saidunhalogenated side groups containing no more than six carbon atoms andno more than one oxygen atom and each of said halogenated side groupscontaining no more than nine carbon atoms.
 2. The polyester of claim 1wherein the average molecular weight is greater than
 500. 3. Thepolyester of claim 2 wherein the main chains of the molecules of suchcompositions having an average molecular weight of 620 or less, passthrough at least 1.2 equivalents of aromatic groups per mole ofcomposition.
 4. The polyester composition of claim 1 wherein at least 52weight percent of the molecules of said composition have a molecularweight of the composition; less than 40 weight percent of the moleculesof the composition having a molecular weight greater than 150% of theaverage molecular weight of the composition and less than 8 weightpercent of the molecules of the composition having a molecular weightless than 50% of the average molecular weight of the composition.
 5. Thepolyester of claim 3 wherein the main chains of the molecules of suchcompositions, having an average molecular weight of 620 or less, passthrough at least two equivalents of aromatic groups per mole ofcomposition.
 6. A polyester composition having an average molecularweight of greater than 500 comprising a most prevalent compound having amain polyester chain containing at least 17 and fewer than 52 carbonatoms and at least 6 and fewer than 18 oxygen atoms, at least 52 weightpercent of the molecules of said composition having a molecular weightwithin 50% of the average molecular weight of the composition, less than40 weight percent of the molecules of the composition having a molecularweight greater than 150% of the average molecular weight of thecomposition and less than 8 weight percent of the molecules of thecomposition having a molecular weight less than 50% of the averagemolecular weight of the composition, said polyester compositioncontaining at least 1.6 equivalents of unreacted hydroxy groups or atleast 1.6 equivalents of unreacted carboxy groups per mole and saidcomposition containing at least four equivalents of ester links in themain chains of the molecules per mole of composition, said compositioncontaining side groups selected from hydrogen and halogenated andunhalogenated groups attached to the main chain through a carbon atom,each of said unhalogenated side groups containing no more than sixcarbon atoms and no more than one oxygen atom and each of saidhalogenated side groups containing no more than nine carbon atomsprovided that, the main chains of the molecules of such compositionshaving an average molecular weight of 620 or less, pass through at least1.2 equivalents of aromatic groups per mole of composition.